⊦ zh = zh0 ↔ (∀ r. (r ∈ zh ↔ r ∈ zh0) ∧ (r ∈ zh → zh[r] = zh0[r]))
zh0 ⊥ zh1, ∀ r. (r ∈ ∅ ↔ r ∈ zh0 ∪ zh1) ∧ (r ∈ ∅ → (∅)[r] = (zh0 ∪ zh1)[r]) ⊦ ¬ r ∈ zh0 ∧ ¬ r0 ∈ zh1
Used terms: zh0 ∪ zh1, ∅